In a cellular type radio network, there are a number of ways of separating the signals transmitted by the transmitter of one cell from those transmitted by the transmitter of an adjacent cell. First and second generation mobile telephone networks used frequency based separation. Here, the network is set up such that transmitters associated with adjacent cells do not transmit on the same frequencies. This works well assuming that there are sufficient frequencies, which leads to its use with narrow frequency bands. A number of frequencies tend to be grouped together, and that group of frequencies is repeated for use with non-adjacent cells across the network. The number of different groups may be between four and fifteen, with seven different groups leading to the honeycomb pattern found in many textbooks.
Third generation mobile telephone systems use a single, wide frequency band, with separation being achieved through the use of different spreading codes.
Within a cell of a Global System for Mobiles (GSM) network, a frequency band is shared between a number of transmitters using time division multiplexing.
All of the above described principles are well known.
It is proposed to provide Internet Protocol Data Cast (IPDC) services as part of digital broadcasting systems such as e.g. the Terrestrial Digital Video Broadcasting (DVB-T) system. The ability to decode data from an IPDC transmission depends on a subscription to that service. To allow reduced power consumption in mobile DVB-T receivers, it has been proposed to transmit IPDC services in bursts utilising the whole of the channel bandwidth, rather than multiplexing them in any other way. This is known as time-slicing. Since DVB-T is a high bandwidth system—each channel may be 6, 7 or 8 MHz wide—the number of available frequencies for cellularisation is quite small. This limits the opportunities for the provision of IPDC services. One way of addressing this is to divide (or rasterise) a DVB-T channel into sub-bands, for example divide an 8 MHz channel into four 2 MHz channels. Cellularisation can then be performed using the sub-bands.
It is an aim of the invention to allow for cellularisation without requiring the division of a channel into sub-bands.